Apparatus for backing workpieces for welding

ABSTRACT

The invention relates to an apparatus for electric arc welding of two spaced plates forming a horizontal weld groove. The apparatus comprises a U-shaped trough which is beneath the weld groove, which extends from one plate to another and which contains a granular refractory material in position to contact the plates along the welding groove, elastic and compressible cushions being interposed between the said granular material and respectively both lateral arms of the U-shaped trough and contacting elastically both plates along these arms, another elastic and compressible cushion being further interposed and elastically compressed between the said granular material and the base of the said U-shaped trough.

United States Patent De Haeck 51 May 9, 1972 [54] APPARATUS FOR BACKINGLa Soudure Electrique Autogene, Prooedes Arcos, Anderlecht, Belgium [22]Filed: June 30,1969

[21] Appl.No.: 837,771

[73] Assignee:

Related US. Application Data [,62] Division of Ser. No. 612,864, Jan.31, 1967, Pat. No.

[30] Foreign Application Priority Data Feb. 11, 1966 Belgium ..23971Sept. 8, 1966 Belgium.. ...33086 Dec. 16, 1966 Belgium... ..37319 [52]U.S.Cl ..2l9/73,2l9/l37,219/160 [51] Int. Cl ..B23k 9/18 [58] FieldofSearch ..219/73, 160, 137; 29/491 [56] References Cited UNITED STATESPATENTS 3,307,014 2/1967 Bada et a1 ..219/73 3,221,135 11/1965Maier,.lr.... ...219/137 2,331,937 10/1943 Schreiner.... .....219/733,420,979 l/l969 Gowan ..219/73 Primary Examiner-J. V. Truhe AssistantExaminer-George A. Montanye Atlarney.lackson, Jackson and Chovanes [57]ABSTRACT The invention relates to an apparatus for electric arc weldingof two spaced plates forming a horizontal weld groove. The apparatuscomprises a U-shaped trough which is beneath the weld groove, whichextends from one plate to another and which contains a granularrefractory material in position to contact the plates along the weldinggroove, elastic and compressible cushions being interposed between thesaid granular material and respectively both lateral arms of theU-shaped trough and contacting elastically both plates along these arms,another elastic and compressible cushion being further interposed andelastically compressed between the said granular material and the baseof the said U-shaped trough.

5 Claims, 6 Drawing Figures PATENTEBW 9 I972 3,662,144

sum 1 OF 2 F'IG.3

1/11/1/{1/1/1/1/11/1/1/1 INVENTOR BY 2 2 M ATTORNEYS P'ATENTEDm 91912 I$662,144

' sum 2 OF 2 ATTORNEYS APPARATUS FOR BACKING WORKPIECES FOR WELDING Thisapplication is a division of application Ser. No. 612,864, filed Jan.31, 1967 for Electric Arc Welding now U.S. Pat. No. 3,51 1,960, grantedMay 12, 1970.

This application relates to an electric arc welding of joints betweenmetallic plates, one of which at least, is laid down.

Plates used in ship building are delivered directly from the steelmills. Their edges are irregular, with jagged seams or covered withoxides. To weld them correctly requires observance of a list of priorconditions. First the edges must become perfectly straight. They aretherefore cut correctly before being abutted. Knowing the number ofplates needed to be welded to make a ship, and that each plate must becut on four sides, one can get an idea of the amount of waste resultingfrom trimming. But there is more: the edges of the plates must be set toavoid any offset between them. They must be level to each other. Thisrequires preliminary positioning which takes a long time.

The complication is still worsened by the fact that when weld metal hasbeen deposited on one side of the joint, the plates must be turned overto deposit weld metal on the reverse side of the joint. This operationis time consuming, difficult and costly because of loss of time.Furthermore it requires capital investment in machinery such as cranesand other material handling equipment and also suitable buildings. Dueto the great dimensions of the plates being welded and this isparticularly true for ship plates the sizes of the workshops becomeinsufficient.

It becomes clear from these facts how advantageous it would be inshipbuilding, to select a welding process which would eliminate allthese difficulties. A desirable feature would be to weld the plateswithout having first to set their edges, and also to weld the plates onone face only.

In addition to the preceding, the following considerations must be takeninto account:

In the technique of shipbuilding, the plate thickness and the welddeposition rate are essential factors. This will explain how importantit will be to use any welding process using higher and higher currentsto increase the deposition rate. Precisely because of the great energydeveloped in the arc of well-known automatic or semi-automatic processesof submerged arc welding, or with flux-cored wires, the latter processesare much in demand in shipbuilding.

When the current increases, the power developed in the arc becomesenormous, and this means also deep penetration in the base metal. Toobtain practical success in an automatic welding process of this kind,two groups of factors must be properly determined the welding parameterswhich a workman of average intelligence can select, and the preparationand setting of the edges.

It is easy to obtain under laboratory conditions a perfect joint by thesubmerged arc welding process in plates V4, i and 1 V4 inches thick andmore, which have been prepared with I, Y or X edges, using theparameters found in most welding handbooks. The plates are placed veryclosely side by side, with some tolerance of the gap between them.Certainly, when the plates have been well sheared, the high currentwelding process is satisfactory. But when gaps between edges to bewelded reach five thirty-seconds inch, the arc and the weld pool maypass through. It is in such case that human control becomes essentialbecause the operator using a manual electrode of the heavy depositiontype will immediately adjust his parameters to suit the variations ofspacing between the edges. It is for that reason that the preparationsmentioned hereabove are often replaced by an incomplete V chamfer withnarrow straight faces at the bottom. One or more passes are hand weldedat the bottom of the chamfer. The joint is then completed with morelayers deposited in succession on one side and the other of these firstmanually welded passes.

In final analysis, the use of a high speed and fully automatic weldingprocess is limited by the practical difficulty of correct pre-assemblingwhich would be compatible with the welding parameters selected in thelaboratory in close relationship to the gap between the edges.

If, however, in spite of these difficulties, high current automaticwelding processes must be used, an improvement can be obtained byincreasing the number of passes and reducing the current in the firstpass. However, there will still be differences in penetration which nolonger can be corrected by the operator because in such case observationand control of the weld pool are missing and therefore the joints willbe of variable quality from the standpoint of interpenetration.Furthermore, the cost of the welding operation will be increased.

To remedy the difficulties of the above-mentioned processes, a cooled oran uncooled metallic back strip, or a refractory one, have beenproposed, such back strip being either powdery or compact. In some casesboth forms have been combined. However, such methods are not usedpractically for the following reasons a thick copper strip such asproposed in Robbins U.S. Pat. No. 3,253,121 to prevent leakage of moltenmetal from the pool is objectionable because of its tendency to cool theweld metal, creating harmful residual stresses in the structure.Furthermore, if the plates being welded are not perfectly plane, andthis is often the case in practice,it is extremely difficult to hold themetallic back strip sufficiently close to the surface of the plates toprevent leakage of weld metal between the backstrip and the rear face ofthe plates being welded. In such case, a spacing between the strip andthe plate of 0.020 inch is the permissible maximum.

Even if it were possible, with considerable care, to reduce greatly thetolerance of level inequality between the plates, variations in the gapbetween the plates which are unavoidable in modern methods of cutting,would still exist. The defects caused by such differences in the gapwidth are the following In the high speed welding process, the weldingparameters are related to high currents. The electric power in the arcis great. When the edges are sufficiently close together, this highenergy of the arc can be distributed correctly and deeper portions inthe joint also become fused, giving a smooth joint on the rear face, butin so doing the penetration effect of the arc extends toward the rearcopper backing strip due to the very power of the arc. If the edges ofthe plates are somewhat wider apart, the penetration effect of the areresults in a local fusion of the copper strip, rapidly followed by alocal cooling, resulting in a heavy contamination of the rear face ofthe weld. The harmful effect of copper in steel, from he backing strip,is well-known in welding practice from the cracking it causes in thejoint. On the other hand if the distance between the edges of the platesis too small, the deeper portions of the joint will be incompletelyfused.

It is therefore clear that the setting of the edges at the correctdistance from each other is a delicate operation which is akin toprecision work with all the consequences it entails in technique, wheresuch requirement becomes a grave drawback.

The harmful effect of the copper can be eliminated by using granularrefractory supporting materials. Such solution has been proposed alreadyby investigators.

Instead of the copper strip covering the rear face of the joint, sometrough, for instance, filled with a free-moving granular refractorymaterial bridges the rear face of the joint. In most variations of thisconcept, the refractory powder is subjected to some pressure against therear face of the parts being welded, in order, allegedly, to give therear face of the weld a suitable profile. In one'of the variants, inparticular, a pneumatic sleeve or tire is placed in the bottom of thetrough and a free metallic strip is located between the sleeve and thepowder filling the trough, to distribute the pressure of the refractorymaterial.

In patent application Ser. No 612,864, now U.S. Pat. No. 3,51 1,960 asindicated, of which the present application is a division, there isdescribed a new granular refractory material allowing a welded joint ofgood quality without the necessity of applying the refractory powderagainst the plates with a high pressure. This granular refractorymaterial is applied against the rear face of the plates, for example bya trough bridging the groove between the .said plates.

However, in case the plates to be welded are not perfectly plane, itbecomes more difficult to pack the refractory powder moderately tightwith pressure against the plates suitable to produce a weld bead showinga satisfactory reinforcement, because the powder leaks out through thegaps between trough and plates. In the case where good pressure beforewelding has nevertheless been obtained, it can happen that duringwelding the said gaps will shrink because of distortion of the platesand/or the trough and that the pressure of the powder against the plateswill become greater than that which would result in a good-lookingreinforcement. It has been found that, in such cases, undercuttingsometimes appears in the plate or the reinforcement changes into agroove.

If, on the contrary, the plates and/or the trough are distorted with theeffect of increasing locally the spacing between trough and plates,thenthe refractory powder which was initially packed tight at thesuitable pressure against the plates ceases to keep contact with thelatter or with one of the plates. It could then happen that the weldpool will flow out laterally and that the reinforcement will take anirregular and poor-looking shape. Furthermore, it has sometimes beenfound that such a reinforcement may be imperfectly welded to the plate.

With a view to remedy these difficulties, the applicant has proposed toapply the said refractory powder elastically against the plates to bewelded. For this purpose, he has proposed a apparatus comprising anU-shaped trough which is beneath the weld groove, which extends from oneplate to another and which contains a granular refractory material inposition to contact the plates along the welding groove. In thisapparatus, elastic and compressible cushions are interposed between thesaid granular material and respectively both lateral arms of theU-shaped trough and contact elastically both plates along these arms.Another elastic and compressible cushion is further interposed andelastically compressed between the said granular material and the baseof the said U- shaped trough.

Thanks to these elastic and compressible cushions, a harmfulover-pressure can easily be avoided during the packing of the powder atthe time of filling the trough, should the amount of powder introducedin the trough be a little greater than what is needed to obtain a nicereinforcement. If, during welding, the gap between the trough and theplates being welded should increase, the elasticity of the compressiblecushion would tend to expand the latter to the initial volume itoccupied before filling, and therefore the powder remains tight againstthe plates. If, on the contrary, the gap between the trough and theplates being welded should be reduced during welding, the resultingover-pressure of the refractory powder against the plates will remainmoderate because the cushion can easily be further compressed.

It has already been proposed to maintain a layer of refractory granuleselastically tight against the plates being welded, by means of apneumatic sleeve set between the bottom of the trough and a freemetallic strip supporting the granules. This method is costly due to theequipment it requires. Moreover, it is very bulky because the layer ofgranules must be thick in order to protect the sleeve against heat.Furthermore, it is sometimes difficult to use because openings needed topass the sleeve must be provided through the stiffeners already weldedon the plates. Finally, it may happen that pneumatic pressure will forcegranules between the plates, especially in locations where the platesare far apart due to careless preparation.

The elasticity of the cushions of the apparatus according to theinvention, which are elastically applied against both plates to bewelded, ensures a good tightness between these cushions and plates, evenwhen the latter are not perfectly plane. Thus, the portions of thesecushions, which contact the plates to be welded, prevent any leakage ofthe refractory powder and contribute to obtain a satisfactory weldedjoint.

In the apparatus according to the invention, the elastic cushionsconsist advantageously of cotton-like felts made of fine fibersresulting from the fusion of a mixture consisting essentially of aluminaand silica with a higher content of alumina than of silica.

The granular refractory material used with the apparatus of theinvention consists advantageously in a mixture of a. 43 to 63% of aningredient comprising 50 to 60% of SiO,,

25 to 3.5% ofCaO, 2 to 4% of MgO, 2 to 4% ofAl O l to 2% of FeO, 0.5 to2% of Na O, 0.5 to 2% of K 0, l to 2% of CaF b. 35 to 50% of aningredient comprising 30 to 40% of SiO,, 55 to 65% of A1 0 and 5 to 10%of various oxides such as CaO, MgO, Fe O TiO,, Na O, K 0;

c) l to 3% of cryolite;

d) l to 4% of a deoxidizer.

The deoxidizers which can be used are, preferably, strong deoxidizerssuch as aluminum, silicon, magnesium, calcium and titanium. Some ofthese deoxidizers may be used in metallic form, others being usable onlyin a combined form. Silicon can be used with advantage.

The invention will now be more fully described with reference to theannexed drawings which represent, as an example, some embodiments of theapparatus according to the invention.

FIG. 1 is a cross section in a U-shaped trough ready to be pressedagainst horizontal plates to be welded.

FIG. 2 is a section across the trough of FIG. 1 after pressing it alonga joint between two horizontal plates to be welded by the submerged arcprocess, the joint being filled with predominently metallic powders plusa layer of welding flux over the joint.

FIG. 3 is a cross-section similar to that of FIG. 1 in the case of thetrough is V-shaped, ready to be pressed against the horizontal platesbeing welded.

FIG. 4 is a section across the trough of FIG. 3 after pressing it alonga joint between two horizontal plates being welded by the visible arcprocess under gas protection, the joint being filled with predominantlymetallic powders.

FIG. 5 is a section across the joint to be welded and the device actingas a support which is a variant on the methods of applying the deviceacting as a support described by the preceding figures.

FIG. 6 is a cross-section of a sub-variant on the method of applying thedevice described by FIG. 5.

In these figures, like references pertain to like means or parts ofmeans used.

In FIG. 1, there is shown a U-shaped trough 6 wherein elastic andcompressible cushions are laid parallel to both flanges or arms of the Uand to the web or base of the same. Said cushions consist in fine fibersof ceramic material compacted to make a cotton-like felt. These fibersare advantageously obtained from a molten mass consisting essentially inalumina and silica, with a higher proportion of alumina than of silica.Fibers having the chemical composition of 51.2% of M 0 47.4% of SiO 0.7%of B 0 and 0.7% of Na O are perfectly suitable to realize the invention.These fibers are obtained, for instance, by blowing high speed gases ona molten mass having the aforesaid composition and heated to atemperature higher than its melting point which is l,760 C. Fibersobtained by this process have a diameter between 2 and 10 microns, theiraverage size being 2.5 microns. They can resist a permanent temperatureof 1,260" C.

They can also be used at higher temperatures of shorter periods of time.

The cushions parallel to the flanges or arms of the trough aredesignated 23. They are arranged with their long faces parallel to theflanges or arms. Upon the web or base of the trough, two cushionsdesignated 23' have been laid with their long faces parallel to the webor base. These cushions 23 are set between the cushions 23 to assistholding the latter against the flanges.

The cushions 23 have a height such as to exceed by a few millimeters theupper level of the edges of the flanges of the trough. The space abovethe cushions 23 and between the cushions 23 is filled completely withrefractory powder. In FIG. 2, the trough filled in this manner ispressed against the lower face of horizontal plates being welded, suchas designated by l and 2 in FIG. 2 The trough is held in such positionby a few weld tacks such as 18. In this setting, the cushions 23 arelightly compressed by their direct contact with the plates, whilecushions 23 are compressed lightly by the pressure they receive from therefractory powder 9. Since these cushions are very compressible, thepressure to which this powder is subjected from the reaction of thecushions remains moderate. Furthermore, due to the great elasticity ofsaid cushions, should the trough separate from the plates duringwelding, the powder would remain in elastic contact with the plates withunchanged pressure. Finally, because the cushions 23 exceed the level ofthe upper edges of the flanges of the trough, they contribute to preventleakage of the powder through a gap which could exist between the platesand the flanges or arms of the trough if these cushions were notinitially higher than these flanges or arms.

In FIG. 2, a predominately metallic powder 12 is shown in the jointbetween the plates being welded. The joint is covered with a layer ofwelding flux l6 intended to permit welding by the submerged arc processwith a fusible electrode such as 15 shown in interrupted lines. By theprocess of the invention, the fusion of said powder in the joint permitswelding the plates with access to one face only, even when the edges ofthe plates facing each other across the joint have not been carefullyset. The refractory powder 9 held in position against the lower face ofthe plates prevents piercing the joint even when the distance betweensaid edges reaches several millimeters. This powder protects thecushions 23 and 23 at the same time against the heat generated by theweld pool during welding. They can thus be used many times before beingreplaced.

In FIG. 3, another trough is shown ready to be pressed against theplates being welded. This other trough is shaped as a V. On bothflanges, elastic and compressible cushions such as 23 have been laidreaching beyond the upper edges of the flanges, upward.

In FIG. 4, said trough is shown being held against the lower face of theplates 1 and 2 by means of wedges 7 engaged between them and U-shapedbraces 13 attached to the plates by a few weld tacks 18 to be removedlater. The edges of said plates have been lightly chamfered even thoughsuch chamfering is not required, as shown in FIG. 4. The welding processshown in FIG. 4, is the visible arc process with gas protection.Processes of automatic welding other than those shown in FIGS. 2 and 4can of course also be used.

The refractory powder 9 used together with the elastic and compressiblecushions as described in FIGS. 1 to 4, may have one of the compositionsdescribed in application Ser. No. 6l2,864, now U.S. Pat. No. 3,5l l,960,of which the present application is a division. For example, this powdermay contain 50 to 60% of Si 25 to 35% of CaO, 2 to 4% of MgO, 2 to 4% ofA1 0 1 to 2% of FeO, 0.5 to 2% of Na o, 0.5 to 2% of K 0, l to 2% ofCaFExperience has shown that there is interest of using as a refractorypowder a mixture consisting of 2 a. 43 to 63% of powder having the abovementioned composition b. 35 to 50% of an ingredient comprising 30 to 40%of SiO,, 55 to 65% of AI O and 5 to of various oxides such as CaO, MgO,Fe,o,, TiO Na O, K 0

c. l to 3% of cryolite v d. l to 4% of a deoxidizer.

Strong deoxidizers are preferably used, such as aluminum silicon,magnesium, calcium, titanium, some of which are usa ble only in combinedform, as in alloys.

Within the limitations mentioned above, the refractory powder mayadvantageously consist of a mixture of 55 percent of the powder as pera) above,with 40 percent of the product as per b) above, plus 2 percentof cryolite and 3 percent sillCOll.

In shipyards, when the metal plates for shipbuilding can be assembled innearby assembly halls prior to being fitted on the ship, the arrangementin which the support at the back of the joint has been made elastic ispreferably used for welding these plates.

The device whereby the support is made elastic is rather cumbersome,however, and efforts are under way to make it as easy to handle aspossible. Among the methods applied to make the device easier to handleis one which consists of reducing the quantity of refractory granules inthe trough placed at the back of the joint, but since this granule layercannot be reduced without unfavorably affecting the quality of the weldbead, an attempt was made to counterbalance the quantity of granuleswithdrawn by interposing a thin strip of braided non-metal fiber betweenthe back of the joint and the trough. (FIG. 5).

During the welding operation the melting of the predominantly metalpowder in thatpart of the joint which is in contact with the fiber stripcauses the latter to melt on the side opposite it, producing a groove.Through the flexibility of the strip of braided non-metal fiber,combined with the elastic effect of the support which enables it toadapt perfectly to irregularities on the surfaces of the plates withwhich it is in contact, this groove has the great advantage of beingperfectly straight and of strictly regular length and depth, for thatpart of the molten metal which is in contact with the groove mouldsitself on the latter and keeps after cooling the shape it thus obtains.

Moreover, when the strip is pierced right through, the surface layer ofthe underlying powder in contact with the strip becomes sintered andmaintains a bottom for the groove.

It is clear, of course, that excessive current levels would causeexcessive melting of the braided strip and part of the underlying powderwith it, which would have the drawback of wiping out the advantage ofusing the strip.

The same would apply if the strip were not thick enough. For thisreason, limiting current and tape thickness values were determined forvarious plate thicknesses within these limits the said results can beobtained.

These values are shown in the table below.

Plate thickness Current in Tape thickness in mm. Amps. in mm. 8 550-6501.5 to 3 15 770800 1.5 to 3 20 850-950 3 to 6 25 10004100 3 to 6 301250-1350 3 to 6 From this table it can be seen that the strip thicknessis a direct function of the current applied, which in turn, of course,is a function of the thickness of the plates to be welded.

A further advantage of this arrangement is that an ordinary refractorymaterial is used as the powder underlying the strip.

As regards the nature of the braided non-metal fiber forming the strip,several types of fiber were used and it was found that silico-aluminoustype fiber, whose melting point is around that of the metal, was verywell suited to the formation of this groove in the strip during-welding.For instance, a fiber which gave especial satisfaction was sillimanitefiber.

The apparatus shown in FIG. 5 comprises a strip 24 of braided non-metalfiber disposed beneath the groove between both plates 1 and 2 to bewelded, which is filled with a predominantly metal powder 12. This strip24 rests on a bed of refractory granules 9 contained in a trough 25.This trough in turn rests on apneumatic tube or tire 26 of elastomericmaterial so that the part of the device acting as a support for thebraided strip exerts an elastic effect from a support not shown and thusprovides the strip with the greatest possible adaptability at the backof the joint to be welded while exerting constant pressure all over.

It may possibly be advantageous to place a thickness of asbestos 27between the trough 25 and the tire 26, to increase the flexibility ofthe device even more. The unit is held in place from the side by rigidflanks 28 and 29. a

The braided strip is about 3 mm thick, and the bed of refractorygranules is also about 3 mm thick.

In the application shown in FIG. 6, trough 25 enters telescopicallybetween the vertical inside walls of casing 30 and rests quite simply ona pair or a double horizontal line of suitable spiral compressionsprings 31 and 32, or on a pneumatic tire (not shown) placed between theouter surface of the bottom of the trough and the inner surface of thebottom of the casing 30.

This application makes it possible to simplify the support device.

The trough is preferably made of copper and fitted, if necessary, withan inside circuit for liquid coolant flow.

What I claim is Q 1. An apparatus for electric arc welding of two spacedplates forming a horizontal weld groove, said apparatus comprisingbeneath the weld groove a U-shaped trough extending from one plate toanother and having lateral walls, a granular refractory material in thesaid trough, and resilient means acting from below for urging the saidrefractory material toward the weld while retained laterally by thelateral walls of said trough, wherein the said resilient means compriseselastic and compressible cushions interposed between the said granularmaterial and respectively both lateral arms of the U-shaped trough andcontacting elastically both plates along these arms, another elastic andcompressible cushion being further interposed between and elasticallycompressed between the said granular material andthe base of the saidU-shaped trough.

2. An apparatus for electric arc welding of two spaced plates fonning ahorizontal weld groove, said apparatus,when in use in suchwelding,comprising:

a. a thin strip of braided non-metallic fibers having a melting pointapproximately equal or higher than the melting point of the material ofthe weld, said strip extending beneath the weld groove, from contactwith one plate to contact with the other one, in position to support andretain the material of the weld, while in the molten state, inside saidweld groove;

b. a granular refractory material underneath said strip and extendingbeneath the weld groove from beneath one plate to beneath the other, inposition to retain said strip against both plates and under said weldgroove;

c. an open-topped U-shaped rigid trough extending across beneath saidweld groove and said strip from beneath one plate to beneath the otherplate and having lateral walls extending along but lower than saidgroove, said trough containing said granular material;

d. resilient means acting from below for urging said refractory materialup in the direction of the weld groove while said material is retainedlaterally by said lateral walls of said trough, whereby said refractorymaterial is urged against said strip.

3. Apparatus of claim 2, in which said strip has a thickness between 1.5and 6 millimeters.

4. Apparatus of claim 2, in whichsaid strip is made of a silicoaluminous substance.

5. Apparatus of claim 4, in which said strip is made of sillimanite.

1. An apparatus for electric arc welding of two spaced plates forming ahorizontal weld groove, said apparatus comprising beneath the weldgroove a U-shaped trough extending from one plate to another and havinglateral walls, a granular refractory material in the said trough, andresilient means acting from below for urging the said refractorymaterial toward the weld while retained laterally by the lateral wallsof said trough, wherein the said resilient means comprises elastic andcompressible cushions interposed between the said granular material andrespectively both lateral arms of the U-shaped trough and contactingelastically both plates along these arms, another elastic andcompressible cushion being further interposed between and elasticallycompressed between the said granular material and the base of the saidU-shaped trough.
 2. An apparatus for electric arc welding of two spacedplates forming a horizontal weld groove, said apparatus,when in use insuch welding,comprising: a. a thin strip of braided non-metallic fibershaving a melting point approximately equal or higher than the meltingpoint of the material of the weld, said strip extending beneath the weldgroove, from contact with one plate to contact with the other one, inposition to support and retain the material of the weld, while in themolten state, inside said weld groove; b. a granular refractory materialunderneath said strip and extending beneath the weld groove from beneathone plate to beneath the other, in position to retain said strip againstboth plates and under said weld groove; c. an open-topped U-shaped rigidtrough extending across beneath said weld groove and said strip frombeneath one plate to beneath the other plate and having lateral wallsextending along but lower than said groove, said trough containing saidgranular material; d. resilient means acting from below for urging saidrefractory material up in the direction of the weld groove while saidmaterial is retained laterally by said lateral walls of said trough,whereby said refractory material is urged against said strip. 3.Apparatus of claim 2, in which said strip has a thickness between 1.5and 6 millimeters.
 4. Apparatus of claim 2, in which said strip is madeof a silico aluminous substance.
 5. Apparatus of claim 4, in which saidstrip is made of sillimanite.